Mtg 20/23: Mon-25-Nov-2024

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Reflection Mapping and Working with Framebuffers

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anyway.
Welcome to
so we're At meeting planning today. I
so there's a choice in your courses that's available now
until the end of the day.
I don't know why I can vote on this. Sometimes it tells me for
other activities that says I can't. I'm not allowed to vote
or give my input,
but here I can. I'm just going to turn off the pictures to like
and look at the responses so far. Do
Is everyone here voted.
So we have pointed responses and 240 to keep the due date today,
five for Wednesday, Five for Friday, and eight for the
following Friday. I
so keep an eye on it that it won't be due today.
So I asked you a question about colors and
reflection.
Now let's take a look at this.
What's going on in this piece of code?
Anyone? Take a look at it?
Anyone starting to feel a seizure coming on or I
I Don't need to make light
of that. Let's do i
Does that make it easier to
interpret What's going On. I
so what do we have? What are you looking at? What's In the scene?
Yes, Q, I,
so how do we decide the colors that we see on the Cube? I
So this is a COVID reflection map. If
QC and
so the cube we see is reflecting The environment from a cube we
don't see the
Okay, so the vertex shader, we're getting the position by
multiplying the vertex after you get from our buffer by the ball
of U and The projection matrix, and then we're getting the eye
position.
It's not the eye position, it's the position of the vertex in
eye coordinates,
and then we are transforming the normal and
by the normal matrix, which is the matrix that we need to
transform normals And object space to normals in our eye
space
and and then
we do
make A call to the GL SL function reflect. So that's
going to give us the information of where, where the reflection
is,
where, from? Where are we going to access the texture?
So there's no i No no colors assigned. Here, no vertex colors
assigned. We're just passing
this
vec three for R for reflection, and in the fragment shader,
we take the reflection R as input and we output the fragment
color. So we're going to use a uniform sampler cube, so we have
a cube map,
and We're determining the fragment color based on the
sample And
that's returned by the texture function, GLSL, if
So how do we specify the texture map to
I Don't know that
picture helps. Does it help or harm both? Okay,
so anyway, that's that's the basic shader, the shaders that
are doing reflection maps. So all everything we see on screen
is the reflection of the environment map.
So
here we're defining the
red, green, blue, cyan, gent and yellow as a union terrain and
so here's the configured texture map. So we're going to create a
texture, and then we're binding texture, as we're using a cube
map. So
create the texture and bind it as a cube map here, and then we
specify the images that Go on
each side.
So we specify the positive x direction,
so positive x gets red, negative x gets green, positive y gets
blue, negative y gets cyan, positive z is yellow and
Negative z Is magenta i
So does that picture make more sense? Now? Let's see. So an
agenda. I
so here We
have Green, Yellow and Blue. We
so We're seeing we're this
corner,
In the reflection. So here's a question. It's a little design
question, maybe, how do we make this code a little more
demonstrative of reflection mapping?
This is clear what's going on from looking at the screen and
the code and
who says it's crystal clear, the textbook author did A great job
creating this sample piece of code. I
It's okay. I
You don't have to You
anyway,
what's going on. Let's
let's do a few more rotations here and see what
so There seems to be an awful lot of magenta. I
so do you have any questions that that we can discuss before
we get To the point of how To improve the code? I
should we leave it here? Who thinks this might be a good I it
question for The final exam you
it. So I mentioned Terminator two already, but I forgot about
the abyss. Anyone seen the abyss?
Okay? That's a good movie to watch. Lots of interesting
special effects. I
So similar to Terminator two.
I, okay, I don't want to give any spoiler, in case you're
going to run out and download not download, but stream or Find
a copy of the Abyss to
to watch the
so the Ideas are reflecting the environment on to the surface
and
so we have
Our view position, a normal and the reflected vector and So
WebGL
tube has only Q maps to work,
so we're determining the
where the reflection reflective vector intersects the texture,
and then that's how we're determining the frame and color
and
so we compute reflection as two times n dot v n minus V
log. Largest magnitude component of r will determine the face of
the cube. The other two components give the texture of
coordinates.
So that gives a bit of explanation of how the colors
are chosen.
So we're putting together six different texture maps.
This is obviously so you Just use texture in GLSL.
So here's The example. Consider to rotate a cube inside a cube
that reflects the color of the walls. If
so this is a cube, as you may have guessed, but It's using
different values of alpha, so The colors of Alpha point five
and
so how Do we make sense of this? I
so that's these are The shaders,
fairly standard. And
Let's look at The colors and
so we have black, red Hill, green, blue agenda, Cyan and
white defined. I
So to enable to set up blending. So we're using Z buffer, so
you've enabled depth test, enable blend, and Then we're
doing source alpha One. Minus source alpha one
so do all sides look translucent And
does this appear like you think it Should? I?
Let's turn off in Service removal and
and there's No indication of whether the inserts rule is on
or off In the interface. That's an issue with sound code and
So here's a simple piece
of code that uses alpha so the
so GL position, again, geo position from the a position and
the vertex color from the attribute color, and pass, pass
those through to the fragment color In the fragment
shader. And you
so I've made yellow opaque and cyan opaque, and the Other ones
are translucent and
so You can see some I
So maybe that makes A little more sense. Do
I want to show you Another
one that's kind
of fun. I
does it look fun?
So here we're using two different texture maps, and
we're updating one from the other, and we're flipping back
and forth.
So this is
think of A game of Life. Maybe I
so if you can see that
this is the picking example that was mentioned earlier. So we can
render into an off screen buffer
and make it easier to read from that buffer the solid colors,
and then we can decide What's going to select. It.
Does that make sense? I
so here we're doing our laying. We're
and our fragment shader we have the
we have, first of all, the vertex color that's passed from
our vertex shader and
and we have the Other face colors, red, green, Blue,
yellow,
cyan and agenda.
So we're using uniform variable u color index.
So if we if it's set to zero, it's just going to pass the
fragment color to the shader. Otherwise, it's going to
the fragment color from the vertex computed by the vertex
shader. If it's set to other than zero, then we're going to
use the
I can explain that better so you color index is an index into the
seven to this seven color array. So the computed color is
position zero, then one through Seven are the primary colors. So
when you color the
me. So I'm not sure why the author has made the if statement
there. I
because we
can just use the in depth color New color index to access All
the seven Colors And
so here we have the List of your mouse down and
so We're going to
to bind a frame buffer. So we're going to draw the scene in
the frame buffer and then read the colors from it.
So here's the read pixels command to get the color and
So if red, so this is red is set and
I always prefer to use braces, so if I
if Red is on, if green is on, If
that doesn't seem like cyan. I
anyway, you can write this more clearly, but the idea is we can
draw a simpler version of the cube in the frame buffer read.
So then when we interact with the frame buffer, we can read
the solid color per face and return that so we know what's
been picked and we can perform the interaction we want to do
with that without having to deal with the complicated or the
complex fragment colors that Come out of the shader. Does
that make sense? I
any questions About the assignments I
any thoughts About that reflection now? I
should it be stopped here for today? I
thank you for today, see you on Wednesday.
Take care. Thank
Take care. Thank

Responses

What important concept or perspective did you encounter today?

The function of gl.blend
Today I learned more about how to map reflections. At first, I thought the program we saw in class was just rotating the outside of a cube while the inside remains at a fixed position. Though I do wonder if that's possible.
About Assignment 3 Extension and Quiz questions discussion
Blending
We looked at the code for reflecting the environment, transparency on a cube, and picking color.
went through reflectionmap code
Mapping
Reflection Map, how reflection maps are being used. Environment mapping, Playing with alpha values of the color in a normal rotating cube example.
environmental mapping, and a method of acquiring colors by rendering in a frame buffer
The concept of how reflection color is used in the cube involves computing the reflection vector in the vertex shader using the reflect function. In the fragment shader, the texture function samples the cube map texture based on this reflection vector to determine the reflected color.
Learn about environment mapping, check reflection map code

Was there anything today that was difficult to understand?

Was there anything today about which you would like to know more?

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